Use of epidural analgesia for surgery (Proceedings)

An "epidural" is defined as an injection into the epidural space, most commonly performed at the lumbo-sacral junction. It was originally used in animals to avoid the use of general anesthetics in aged debilitated and shocky animals back when anesthetic choices were more limited and more dangerous than the options we have today. It is more commonly used today as an analgesic adjunct to general anesthesia to provide excellent pain control and to avoid the systemic effects of some pain medications. There are several reasons why an epidural works. It has direct action on the spinal cord which accounts for most of it's analgesic activity. It can also migrate to the nerve roots and there can be some systemic uptake of the drugs.

There are many applications for the use of an epidural. Amputations, fractures, urogenital surgery, obstetrics, anal sac disease and almost any painful condition caudal to the umbilicus. The uses in these areas are for intra operative and post operative pain control. There are also certain conditions in which an epidural should be avoided including, animals with a coagulopathy, pyoderma in the area of injection, septicemia, hypotension and certain neurological conditions. Always consider reduced drug dosages in animals that are aged, obese or pregnant

Equipment and Drugs. The equipment needed is minimal and includes sterile drape, sterile gloves, spinal needle and syringe. Drugs most commonly used are preservative free morphine, bupivacaine, and dexmedetomidine.

Procedure. The animal can be placed in lateral or sternal recumbency. I find sternal recumbency easier. Draw the legs forward, if pathology allows, in order to slightly open the sacral canal. After a surgical prep of the lumbo-sacral region, the sacral canal is located by palpation and a spinal needle is inserted with the bevel of the needle facing the direction you most want to affect. In dogs, the needle is inserted at about a 30 degree angle, in cats about 45 degrees with the point of the needle facing cranially. The needle is inserted through the tough fibrous layer and stopped. At this point, remove the stylet and you should be able to insert a small amount of air without resistance. If you get CSF fluid back, then you have gone too far and need to withdraw the needle a bit. If you hit bone while advancing the needle, check your position and angle and reinsert. If you hit blood, you have probably hit the venous sinus and you should withdraw the needle. Now take the syringe with the drugs in it and attach it to the needle, leaving a small bubble of air in the syringe. The injection should be done slowly over 2-3 minutes. If the bubble compresses during slow injection, you are probably out of the epidural space and need to reposition.

Complications. Motor weakness which is somewhat dose related. This usually resolves within a few hours up to 24 hours. Urinary retention which can be quite painful to the animal. Visually watch an animal urinate and then palpate the bladder for fullness before releasing to client care. Pruritis. Nausea. Hypotension. Apnea secondary to the block reaching the level of the phrenic nerve...elevating the cranial half of the body after injection can help prevent this, slow injection can help prevent this. Meningitis secondary to infection or drug inflammation (Never use formalin preserved drugs, choose preservative free when possible). Bleeding. Block failure which happens in up to 15% of all blocks regardless of technique.

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